Oil tank heating apparatus

ABSTRACT

A movable unit for heating cargo oil carried in the holds or tanks of a vessel, the unit, when required, being disposed on the base of the hold or tank and connected to main steam lines and drain lines of the vessel by removable connections. The unit includes a wheeled carriage which permits it to be moved into and stored in a housing at the base of bulkheads between the holds or tanks, and is sealed therein when the holds or tanks are used for transporting dry bulk cargo.

United stateS Patent Campbell et al.

[ June 12, 1973 1 OIL TANK HEATING APPARATUS [75] Inventors: George Thomas Richardson Campbell, Moritomo Wakamatsu, Nishi, both of Tokyo, Japan [73] Assignee: Algoship International Limited,

Nassau, Bahamas 22 Filed: Jan. 26, 1971 21 Appl. No.: 109,795

[52] US. Cl 114/73, 114/72, 165/74 [51] Int. Cl B63b 25/02 [58] Field of Search 114/72, 73, 74 R,

[56] References Cited UNITED STATES PATENTS 2,615,687 10/1952 Simmons ..165/74X FOREIGN PATENTS OR APPLICATIONS 1,218,880 l/l97l Great Britain.... 114/73 1,070,027 5/1967 Great Britain.... 114/73 Primary Examiner-Milton Buchler Assistant Examiner-Stuart M. Goldstein Attorney-Fetherstonhaugh & Co.

[5 7] ABSTRACT A movable unit for heating cargo oil carried in the holds or tanks of a vessel, the unit, when required, being disposed on the base of the hold or tank and connected to main steam lines and drain lines of the vessel by removable connections. The unit includes a wheeled carriage which permits it to be moved into and stored in a housing at the base of bulkheads between the holds or tanks, and is sealed therein when the holds or tanks are used for transporting dry bulk cargo.

7 Claims, 22 Drawing Figures Pmmmm 3.138.305

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SHEEI 8 0f 7 INVENTORS G. T. R. CAMPBELL M. WAKAMATSU PA ENT AGENTS PATENT EB JUN T 2 1975 SHEET'JNT INVENTORS G. T. R. CAMPBELL M. WAKAMATSU ON M PATENT AGENTS OIL TANK HEATING APPARATUS This invention relates to oil tank heating apparatus particularly for use in the tanks or holds of bulk cargo vessels convertible to either oil or dry cargo.

ln dual purpose cargo vessels which are adapted for the transportation of bulk oil or dry cargo, it has been a serious problem to provide suitable heating apparatus for maintaining oil cargo at the right temperature considering the temperature of the water within which the vessel is operating, and at the same time to provide stowage of the heating apparatus out of harms way when dry bulk cargo is being carried. When a changeover from fluid to dry cargo takes place, the heating apparatus has had to be disconnected from the main heat supply system, sealing off the heat supply system and removing the hold heating apparatus to a safe location where it will not be damaged by the bulk dry cargo and the unloading apparatus used to remove the dry cargo from the vessels hold.

The heating apparatus conventionally installed in the hold of bulk/oil carrier vessels consists of a large flat rectangular heating unit incorporating in it the heating pipe. This unit is installed on the bottom of the ship and it is designed to heat the cargo oil by connecting with the unit steam supplying pipe and drain pipe from the deck. The dimension of the conventional heating unit is a rectangular of 6 M X 4 M having a thickness of 40 CM and a weight of 2 3 tons. Such heating unit is lifted up to underneath the hatch cover and fixed thereto by securing bolts etc., when it is not in use, i.e., when ship carries coal, ore, grain and etc.

However, such method has the following shortcomings.

It is dangerous and consumes considerable labor by the crew to lift up or down such a heavy unit weighing of up to 3 tons. Installation of the unit on the ship tank topv also requires considerable labor and materials. Holes must be provided in the hatch covers for the work of stowing the unit and for securing it in place under the hatch cover. The holes in the hatch covers involve special counter-measure and equipment to make the hatch covers watertight. This invention has been developed to resolve these problems.

The present invention is designed to. overcome the above disadvantages by providing means whereby the heating unit can be stowed within a compartment forming a part of the bulkheads separating the holds from each other, the compartment being located at tank top level at the bottom of the hold. The heating unit can be located as a fixed unit within the bulkhead compartment, with provision to effect circulation of the cargo oil through the heating unit, or it can be a movable unit withdrawable from the bulkhegd compartment into the hold when oil cargo is being carried and sealed within the bulkhead compartment when bulk dry cargo is being carried.

In order to facilitate the rapid movement of the heating unit from one position to the other it can be provided with a wheeled carriage for movement on a set of rails. The opening from the cargo hold to the bulkhead compartment is provided with an oil-tight seal in order to protect the heating unit from damage when bulk dry cargo is carried in the hold of the vessel.

Where the heating unit is a fixture within the bulkhead compartment, provision is made by means of lower and upper parts of the compartment to permit circulation of the cargo oil over the heating unit, and closure caps or doors are fitted to the lower and upper parts of the compartment to prevent entry of the bulk dry cargo when such cargo is carried. Provision is also made whereby these closure doors can be moved to the open or closed position by means of suitable mechanism operable at deck level.

Similar heating apparatus can be used in oil only tanks in a vessel, such as in settling tanks, such units being provided with a large flange whereby the unit can be inserted into the tank through a suitable apertured and sealed in place by securing the flange to the wall of the tank around the aperture. Such heating units can be replaced rapidly in place of the time consuming operation of disconnecting and sealing off heating grids at present in use which are bolted to the inside surfaces of the tank walls.

The object of the invention is to provide a novel and efficient heating unit for installation in oil tanks, in which the unit is provided with inlet and return line connections and can be readily installed within an oil tank for heating of the tank contents or be quickly withdrawn from the tank for maintenance purposes.

The object of the invention is to provide oil cargo heating apparatus for use in multi-purpose vessels, which can be exposed for heating of cargo oil or sealed from contact with bulk dry cargo.

A further object of the invention is to provide an economical method and apparatus for heating cargo oil in a dual purpose vessel, which can be rapidly exposed to the cargo oil or isolated from bulk dry cargo.

A further object of the invention is to provide a heating unit storage compartment in the bulkheads separating the cargo holds from each other, the storage compartment being located at the level of the bottom of the cargo hold.

A further object of the invention is to provide means to circulate cargo oil through a heating unit storage compartment within a vessels bulkheads.

A further object of the invention is to provide a heating unit which can be connected to or disconnected from the vessel's heating system without the necessity of having long lengths of piping which has to be removed from within the vessels hold.

While the invention will be described and illustrated with particular reference to oil cargo vessels, it is to be understood that it can be applied to oil storage tanks on land with the particular advantage that the heating unit can be inserted into and be withdrawn from a storage tank through any suitable opening in the tank wall, with the further advantage that all heating medium lines are connected to the unit externally of the storage tank and that no internal anchoring means are required within the tank. With such an installation, there is no necessity for maintenance personnel to enter the tank for the purpose of securing or releasing fixed heating grids with a resulting greater safety of operation.

These and other objects of the invention will be apparent from the following detailed specification and the accompanying drawings in which:

FIG. 1 is a diagrammatic longitudinal section of a ships hold showing a conventional method of heating a hold carrying a cargo oil with the heating unit being secured to the tank top surface and the means for raising the heating unit for stowage under the hatch cover.

FIG. 2 is a plan view of the installation shown in FIG. 1.

FIG. 3 is a perspective view showing a typical installation of one form of heating unit according to the present invention.

FIG. 4 is a partial longitudinal section of a vessels bulkhead at tank top level showing in full lines the heating unit of FIG. 3 in stowed position within a bulkhead compartment, and in chain dot lines the unit in oil heating operative position.

FIG. 5 is a plan view taken on the line 5-5 of FIG. 4.

FIG. 6 is a front elevation taken on the line 6-6 of FIG. 4.

FIG. 7 is a partial longitudinal section through a bulkhead showing a modified form of cargo oil heating unit.

FIG. 8 is a front elevation of the installation shown in FIG. 7 taken on the line 8-8.

FIG. 9 is an enlarged sectional view of the heater unit shown in FIGS. 7 and 8.

FIG. 10 is a transverse section taken on the line 10-10 of FIG. 9.

FIG. 11 is a partial view similar to the lower portion of FIG. 7 but showing a modified form of heater unit.

FIG. 12 is a partial view similar to the lower portion of FIG. 8 but showing the heater unit of FIG. 11.

FIG. 13 is an enlarged vertical section of the heater unit shown in FIGS. 11 and 12.

FIG. 14 is a transverse section taken on the line 14-14 of FIG. 13.

FIG. 15 is an enlarged vertical section of the upper portion of the installation shown in FIGS. 7, 8, 11 and 12.

FIG. 16 is a phantom perspective view of an oil tank such as a settling tank, showing a conventional form of a coil heater unit.

.FIG. 17 is a vertical section of the oil tank shown in FIG. 16 but showing the installation of a fixed heater unit insertable in the tank through one wall thereof.

FIG. 18 is an enlarged side elevation of the heater unit shown in FIG. 17.

FIG. 19 is a front elevation of the heater unit shown in FIG. 18.

FIG. 20 is a vertical section taken on the line 20-20 of FIG. 18.

FIG. 21 is a vertical section taken on the line 21-2l of FIG. 18.

FIG. 22 is a vertical section taken on the line 22-22 of FIG. 18.

Referring to the drawings and particularly to FIGS. 1 and 2 there is shown a conventional form of heating bulk oil in the holds of a cargo vessel. In this arrangement the conventional heating unit 5 is assembled in a frame 6 of about 6 M X 4 M X 0.4 M fitted at the bottom of the hold. The heating unit 5 consisting of a series of U pipes is connected at one end to the steam supply pipe 7 and at the other end to the drain pipe 8. The whole unit 5 is held down on the tank top 9 by a series of securing bolts 10.

When the heating unit 5 is not required for the heating of cargo oil such as when the hold is to be used for bulk dry cargo it is necessary that the heating unit be removed in order not to be damaged by the dry cargo and the apparatus used for stowage of the dry cargo and for removing such cargo as at the end of a voyage. In such case a number of accessory fittings and machinery is required to lift the heating unit up and to secure it on the under surface of the hatch cover 11. This includes lifting ropes l2, guide ropes 13, both passing through holes in the hatch cover 11, a winch on deck for lifting the heating unit 5, and all means to seal the opening in the hatch cover 11 when the heating unit is secured on the hatch cover underside.

When the heating unit 5 is used in the tanks of tanker vessels it is fixed permanently on the bottom of the tank without protection against damage. 1

Referring now to FIGS. 3 to 6 inclusive a compact heating unit 15 consists of a series of pipes 16 located between end plates 17 and 17a, the pipes 16 being connected together by U connections 18 to form one continuous heating medium circuit, having a steam inlet connection flange l9 and an exhaust outlet connection flange 20 both located outwardly of the end plate 17. The inlet and outlet connections flanges 19 and 20 are preferably located adjacent the end plate 17.

Each of the end plates 17 and 17a constitute a trolley joined together by the pipes 16, and each trolley is fitted with a pair of wheels 21 and 21a running on the rails 22, located within the compartment 23, and run directly on the tank top 9 of the vessel when the heating unit 15 is being moved to the withdrawn position.

The rails 22 are laid on the tank top 9 within a housing 23 built into the bottom ramp portion 24 of the transverse bulkheads 25 of the vessel to permit the heating unit 15 to travel in the direction of the arrow 15a. In one position, the heating unit 15 is completely housed within the housing 23 when not used for heating purposes and is protected against bulk dry cargo by the closure doors 26. When the heating unit is withdrawn from the housing 23 into the hold of the vessel, as shown in chain dot lines in FIGS. 4 and 5, connection is made to the main steam and exhaust lines 27 and 28 of the vessel through the flange connections 19 and 20 by removable steam and drain pipes or hoses 19a, 20a.

In place of the closure doors 26 the end plate 17a may be enlarged overall to form a closure plate and be secured to the surface of the ramp 24 by suitable fastening means, and be provided with hand grips 29, or alternatively by suitableeyebolts to which a pulling tackle can be attached. The end plate 17a is also provided with brackets 30 by means of which the heating unit can be secured to the tank top 9 by means of suitable set screws threaded into the inserts 31 in the tank top 9 when the unit is withdrawn from its housing into the hold (FIG. 4).

The end plate 17 is provided with a bracket 32 having an aperture 33 to receive a fastening bolt whereby the unit can be secured within the housing 23 to a suitable anchorage, not shown.

A stop 34 on the ends of the rails adjacent the entrance to the housing 23 limits the travel of the heating unit 15 out of the housing 23 and into the hold of the vessel, and is placed on the rails after the wheels 21a have cleared the rails. This limitation of the travel of the heating unit permits the use of short fixed lengths of pipe connections between the flanged connections 19 and 20 of the heating unit and the main steam and exhaust pipes 27 and 28 when the unit is in operative position within the hold and external of the housing 23.

In the operation of the above described apparatus, when bulk dry cargo is being carried in the hold of the vessel, the heating unit 15 is secured against movement within the housing 23 and the compartment is sealed by means of the closure doors 26 or by securing the heating unit end plate 17a against the entrance to the housing 23.

When oil cargo is being carried, the heating unit is moved out of the housing 23 and is secured to the bottom of the hold at 31, the necessary pipe connections are then made between the connections 19 20 and the pipes 27 28. The flow of steam through the pipe can then be started and drained through the pipe 28.

Convectional circulation is started in the cargo oil and the circulation will be up adjacent to the nearby bulkhead and outwards to the center of the hold and then back along the bottom of the hold towards the heating unit. It is to be understood that more than one heating unit can be installed at each bulkhead in the manner described, one on the side of the bulkhead as illustrated and facing outwards from the opposite side of the bulkhead so that convectional circulation of cargo oil can be directed from both bulkheads in a hold, outwards towards the center of the hold.

The movable heating unit 15 above described may be replaced by a fixed heating unit as illustrated in FIGS. 7 to 10 inclusive. This heating unit 35 is located within the ramp housing 36 at the foot of the cofferdam 38 formed by the transverse bulkheads 37 and 37'.

The heating unit 35 consists of a housing 39, an oil inlet duct 40 connecting the housing 39 with the hold at an opening 41 in the wall of the ramp housing 36, and a duct 42 placed vertically within the cofferdam 38 and connected at its lower end with the heater housing 39 and, at its upper end, connecting with the interior of the hold of the vessel through the opening 43 in the bulkhead 37'. The opening 41 in the inlet duct 40 is provided with a closure cap 44, while the opening 43 from the duct 42 is provided with a closure cap 45. The closure cap 45 is moved into the closing position from the open position by means of the rod 46 operable by the handwheel 47 at deck level. The shaft 46 is passed through the airtight gland 47a at deck level.

The housing 39 is shown as being cylindrical and is disposed at an angle of 45 inclination from a horizontal line. This is for convenience of ensuring that the circulation oil from the hold pervades evenly around the heater pipes 48a to absorb maximum heat.

A heat exchange element 48 is mounted within the housing 39 and consists of a series of parallel pipes 48a connected together at their ends by U bends 49 to form a continuous steam path. One end of the heat exchange element 48 is connected by means of the pipe 50, to the main steam supply system while the opposite end of the element is connected by means of the pipe 51 to the system drain. The pipes 48a are provided with fins or more efficient heat transfer.

Means to wash out the housing 39 and the heat exchange element 48 consists of a series of perforated pipes 52 located between the pipes 48a. Wash water is supplied to the perforated pipes 52 through the supply pipe 53 and the control of the flow of wash water is by means of a remote control valve, not shown.

When the caps 44 and 45 are opened, and the heating unit is activated, a circulation of oil from the lower part of the hold, through the heater and into the upper part of the hold, is effected in order to maintain the temperature of the cargo oil at a suitable level to counteract the temperature of the water in which the vessel is passing through.

A modified form of fixed heater is shown in FIGS. 11 to 14. In this form the heat exchange pipes are not finned, as is the case with the heat exchange pipes 48a in FIGS. 9 and 10. In this form the heat exchange housing 54 consists of a lower cylindrical portion 55 and a conical upper portion 56. An oil inlet pipe 57 connects the interior of the hold with the lower portion 55 of the heat exchanger, and a duct 58 connects the top of the conical upper portion 56 with the top area of the hold in the same manner as the duct 42 in FIGS. 7 and 8. The inlet pipe 57 and the duct 58 are provided with closure caps 59 and 60 also in the same manner and for the same purpose as in FIGS. 7 and 8.

The heat exchange coils, without fins, are shown in three banks 61, 62 and 63, and are supported in place in axial alignment with the housing 54 by the frame 64. Steam supply pipes 65 feed steam to each of the three banks of coils 61, 62 and 63 respectively while the drain pipes 66 drain the banks of coils.

Wash water for cleaning out the housing 54 and the banks of coils 61, 62 and 63 is supplied through the supply pipe 53 and perforated pipes 52 in the same manner as is shown in FIGS. 7 to 10.

In order to improve the efficiency of the heat exchangers 35 and 54 by circulating the cargo oil forcefully through the heat exchangers, an impeller 66 may be fitted in the ducts 42 and 58 in the manner shown in FIG. 15. The impeller 66 is fitted to the lower end of the shaft 67 which is supported in the bracket 68 and in the gland 69. The shaft 67 extends upwards through the deck through the gland 70 and is driven by the motor 71 through the reduction gear unit 72.

In all of the above described apparatus the circulation of oil from the bottom of the hold or tank is directed to the upper part of the same hold or tank. Where the cofferdam separates two holds or tanks, the cofferdam will include two or more oil heating and circulating units some of which are directed to one hold on one side of the cofferdam and others directed to the hold on the opposite side of the cofferdam.

The operation of the invention is illustrated in FIGS. 7 to 15 is as follows.

If the cargo oil is loaded in the holds or tanks and the caps 44 and 45 or 59 and 60 are opened, the ducts 42 and 58 are also filled with cargo oil. If heating is commenced by supplying steam to the heat exchange elements positioned within the housings 39 or 55-56, which, in effect form part of the ducts, the cargo oil around the heat exchange elements is heated and its specific gravity is reduced. The heated oil then ascends through the duct and is discharged into the upper part of the hold or tank, and in turn, low temperature cargo oil flows into the heat exchanger through the duct 40-57 thus generating a natural convectional circulation.

Convectional circulation speed of oil is related to difference of specific gravity of heated and unheated oil, height of duct, etc. however, convectional circulation speed is higher by the use of the heating units above described than is the case of normal heating coils which are arranged flat on the bottom of the holds or tanks in oil tankers in immediate contact with a large mass of cargo oil. Consequently, the invention of the present application, where heat transmission between the heat exchange element and the cargo oil is exceptionally high, the efficiency over the normal method ensures that the oil temperature of the cargo oil will be maintained at a minimum of cost.

If the oil tank heating apparatus of this invention as shown in FIGS. 7 to 15 is installed in a combination carrier of oil and ore, it is only necessary to open the upper and lower openings of the conduit installed in the cofferdam type bulkhead, and to supply steam to the heat exchange element of the heater, effect efficient heating of the cargo oil by convectional circulation of the oil.

When bulk cargo such as ore is loaded in the oil hold or tank, the only necessary step to be taken is to ensure that the duct closure caps 44-45 or 59-60 are closed and made oiltight, and to ensure that the steam and drain connections to the heat exchangers are broken and closed off after having washed the oil hold or tank and the inside of the ducts and heat exchangers with heated salt water and to ensure that the main steam and drain connections are closed off. The cap closing the lower duct 40-57 can be reached easily to fix in place while the cap closing the upper end of the duct can be readily closed by means of the handwheel at deck level. Consequently, the complicated and expensive handling, such as dismantling, transportation and stowage of heating pipes on the bottom of holds or reinstallation of the pipes of the installation as is illustrated in FIGS. 1 and 2, each time the kind of cargo changes as in the case of conventional combination carriers, is no more necessary. The replacement of the installation as shown in FIGS. 1 and 2 of the installation above described contributes to a large extent to rationalization of a ships operation and labor saving in cargo handling.

In the case of vessels now in use and not having a cofferdam type of bulkheads the heating apparatus illustrated including the necessary ducts can be installed in the oil tanks against the bulk heads at little cost and will result in higher efficiency than is the case with conventional heating apparatus, and because the large expense of transportation, fitting and unfitting of heating units and associated piping are no longer necessary.

Heating units such as are illustrated in FIG. 3 can be used to advantage in closed oil tanks, such as fuel oil settling tanks, in place of the heating units now generally in use, as shown in FIG. 16.

In FIG. 16 heating coil units 70 of the type now in use are fastened to the inner walls of the tank 71 in the form of grids, and steam and drain connections 72 and 73 are made through the walls of the tank.

Generally the fuel oil in settling tanks and in service tanks is required that the oil temperature be raised to between and centigrade within 24 hours, therefore the heating ratio required for fuel oil is greater than the heating of cargo oil. Consequently, the heating tubes such as the units 70 are arranged more crowded than would be the case when heating cargo oil. Therefore, the installation of the heating coil units 70 in the confined space of settling tanks causes difficulties both in installation and in maintenance and repair.

Heating units such as are illustrated in FIG. 3 can be used to advantage in closed oil settling tanks. Such an installation is shown in FIGS. 17 and 18.

In this arrangement the compact heating unit 74 consists of a series of parallel pipes 75, preferably having fins 76. The pipes 75 are joined at their ends by U bends 77 to form a continuous steam flow path. The two ends of the continuous flow path consists of extension pipes 78 and 79 which are welded at their midportion to a support bracket 80.

This support bracket 80 consists of a front facing plate 81 through which the extension pipes 78 and 79 pass and to which they are welded to at the mid-portion of their length, a series of inwardly extending plates 82 and an inner support plate 83 disposed parallel to the facing plate 81 and supporting the adjacent end portion of the pipes to hold these pipes in their spaced apart relationship.

At the opposite end of the heating unit 74 a support plate 84 similar to the support plate 83 hold the pipes 75 in their spaced apart relationship.

A foot bracket 85 is welded to the lower edge of the support plate 84 in order to rest against the lower wall 86 of the tank 71a.

The front wall 87 of the tank 710 is provided with an aperture 88 through which the heating unit 74 is inserted into the tank, and the front facing plate 81 is bolted around its periphery to the wall 87 to provide an oiltight seal.

With this form of heating unit 74, the installation of the unit will be completed instantaneously by inserting the unit through the aperture 88 and bolting the front face plate 81 in place. It is then only necessary to connect the extension pipes 78 and 79 to the main steam and drain lines of the vessel.

A high degree of efficiency in heating of the fuel oil will be attained as the ascending oil first heated by the lower portion of the heating unit will be increased as the oil flows over the upper portion of the heating unit. The increased efficiency will be much higher than that produced by heating coils secured to the inner surface of the tank walls as shown in FIG. 16.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. In a dual purpose bulk oil and dry cargo vessels having transverse bulkheads separating the holds or tanks of the vessel, said transverse bulkheads including a housing at the base thereof, heating units for heating oil carried by the vessel, said heating units comprising a steam coil having steam and drain connections, removable means to couple and uncouple said heating units to main steam and drain lines of the vessel, said heating units being mounted on a wheeled carriage for movement of the heating units between an oil heating location on the base of the holds or tanks and a storage location in which the heating units are disposed in the housings in said bulkheads when bulk dry cargo is carried in the holds or tanks, and securing means to selectively secure the carriages of the heating units within said housings and at fixed locations in the base of the holds or tanks.

2. In dual purpose vessels as set forth in claim 1 wherein said housing is provided with rails, and closure doors of the housing seal said heating unit within the housing when dry cargo is carried within the holds or tanks of the vessel.

3. In dual purpose vessels as set forth in claim 1 wherein said securing means include apertured brackets provided in said heating units whereby the same may be secured to the bottom of the holds or tanks externally of the housing.

4. In dual purpose vessels as set forth in claim 1 in which removable steam and drain pipe connections connect said heating units with main steam and drain system of the vessel when the said heating units are located in the base of the holds or tanks of the vessel.

5. In dual purpose vessels as set forth in claim 1 in which the said wheeled carriage includes a pair of opposed end plates supporting between them said steam coil, and one of said end plates form an oil-tight seal main steam and drain lines are connected when the heating units are located in the holds or tanks of the vessel.

7. In dual purpose vessels as set forth in claim 6 in which the straight pipes between the end plates are provided with fins and the pipes laid in courses one above the other. 

1. In a dual purpose bulk oil and dry cargo vessels having transverse bulkheads separating the holds or tanks of the vessel, said transverse bulkheads including a housing at the base thereof, heating units for heating oil carried by the vessel, said heating units comprising a steam coil having steam and drain connections, removable means to couple and uncouple said heating units to main steam and drain lines of the vessel, said heating units being mounted on a wheeled carriage for movement of the heating units between an oil heating location on the base of the holds or tanks and a storage location in which the heating units are disposed in the housings in said bulkheads when bulk dry cargo is carried in the holds or tanks, and securing means to selectively secure the carriages of the heating units within said housings and at fixed locations in the base of the holds or tanks.
 2. In dual purpose vessels as set forth in claim 1 wherein said housing is provided with rails, and closure doors of the housing seal said heating unit within the housing when dry cargo is carried within the holds or tanks of the vessel.
 3. In dual purpose vessels as set forth in claim 1 wherein said securiNg means include apertured brackets provided in said heating units whereby the same may be secured to the bottom of the holds or tanks externally of the housing.
 4. In dual purpose vessels as set forth in claim 1 in which removable steam and drain pipe connections connect said heating units with main steam and drain system of the vessel when the said heating units are located in the base of the holds or tanks of the vessel.
 5. In dual purpose vessels as set forth in claim 1 in which the said wheeled carriage includes a pair of opposed end plates supporting between them said steam coil, and one of said end plates form an oil-tight seal member to isolate and seal the heating unit in said housing from the cargo hold or tanks when dry bulk cargo is carried in the vessel.
 6. In dual purpose vessels as set forth in claim 5 in which the said steam coil comprises a series of straight pipes supported between spaced apart end plates and U bends connect adjacent ends of the straight pipes to form one continuous coil and the ends of the continuous coil are provided with flange connections to which main steam and drain lines are connected when the heating units are located in the holds or tanks of the vessel.
 7. In dual purpose vessels as set forth in claim 6 in which the straight pipes between the end plates are provided with fins and the pipes laid in courses one above the other. 